Re: picking a mattress when you have myofascial pain
A good mattress can be an investment. Check out multiple before making such a purchase and insist on lying on the mattress for an extended period. (Figure out how long you are able to lie in your current bed before you sense discomfort and use that as a guideline on how long you need to lie on the demo beds.) I don't know about the quality of their mattresses, but I think Ikea gives you a 90-day trial period. I kind of wonder what they do with those mattresses, once they are returned.
You might try a couple of back/ergonomic stores. They often have dealt with folks with similar issues and may have recommendations. You might be able to use health savings account money to assist with your purchase, if your employer has such a program. Many stores also offer extended interest-free payment periods, but read the fine print on these offers.
I use a memory foam wedge, from a back store, under my knees to alleviate lower back pain, and it helps me a lot.